Depth of field for the presbyope.

As a general rule the near addition (add) for a presbyope is selected so that the range of clear vision is dioptrically and not linearly balanced. Implicit in such thinking is the assumption that the dioptric and linear range of clear vision cannot be simultaneously balanced. Assuming that the range of clear vision for the absolute presbyope is due to depth of field and assuming also that the blur circle theory adequately describes the limits of depth of field, I will show that the dioptric and linear range of clear vision can indeed be simultaneously balanced. The results are independent of the actual position of the reference plane from which the measurements are made.